FreeBSD Security Advisory FreeBSD-SA-02:31.openssh

FreeBSD Security Advisories security-advisories at
Mon Jul 15 10:02:08 PDT 2002


FreeBSD-SA-02:31                                            Security Advisory
                                                          The FreeBSD Project

Topic:          openssh contains remote vulnerability

Category:       core
Module:         OpenSSH
Announced:      2002-07-15
Credits:        ISS X-Force <xforce at>
                Theo DeRaadt <deraadt at>
Affects:        FreeBSD-CURRENT between 2002-03-18 and 2002-06-25
Corrected:      2002-06-25 19:10:07 (HEAD)
FreeBSD only:   NO

I.   Background

OpenSSH is a free implementation of the SSH protocol suite, and
provides encrypted and authenticated remote login, file transfer and
command execution.

II.  Problem Description

SSH clients and servers communicate by exchanging discrete messages
with a variable number of parameters.  Due to the lack of sufficient
integrity checks in a portion of the server code responsible for
handling incoming SSH2_MSG_USERAUTH_INFO_RESPONSE messages, it was
possible for a malicious client to send a message that would cause the
server to overwrite portions of its memory with client-provided data.

III. Impact

An remote attacker using an SSH client modified to send carefully
crafted SSH2_MSG_USERAUTH_INFO_RESPONSE to the server could obtain
superuser privileges on the server.

Please note that this problem only affects FreeBSD-CURRENT.  No
versions of FreeBSD-STABLE are or were ever vulnerable to this bug.

IV.  Workaround

Do one of the following:

1) Disable SSH entirely.

2) Use a firewall to block incoming SSH connections from untrusted

3) Add the following line to /etc/ssh/sshd_config, and restart sshd.

ChallengeResponseAuthentication no

   Note that this will prevent the use of OPIE and similar challenge-
   based authentication methods with SSH.

V.   Solution

Update your system to the latest -CURRENT.

VI.  Correction details

No correction details are provided in this advisory.

VII. References

Version: GnuPG v1.0.7 (FreeBSD)
Comment: FreeBSD: The Power To Serve


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